It is known to treat troubles of the cardiac rhythm (arrhythmias) with cardiac stimulation. It also has been proposed to treat troubles of the myocardium contraction observed in patients with cardiac insufficiency (hereinafter "troubles") with cardiac stimulation. These latter troubles can originate spontaneously or can be induced by a traditional cardiac stimulation impulse. Reference is made to the study of J. C. Daubert et al., Stimu.oe butted.ur, Volume 25, n.degree.3, pp. 170-176 (1997) which describes the state of the art on this subject. It has already been proposed to stimulate simultaneously the right and left ventricles, which is known as a "double stimulation". This technique also can be applied to a double stimulation of the atria (i.e., the left and right atria).
One of difficulties of the known multisite stimulation is to guarantee the efficiency of the stimulation on the different cardiac sites. In particular, one generally observes different stimulation thresholds between the right site and the left site. This can result in a defective (e.g., insufficient) stimulation or an erroneous depolarization wave detection (i.e., confusion between an electro-stimulated depolarization originating at the one site and an indirectly sensed depolarization having its origin at the neighboring site). The latter is sometimes called a "far-field" detection.
French patent FR 2 680 093 and its corresponding U.S. Pat. No. 5,411,533, commonly owned by the assignee of this invention, describe a device provided with an automatic adjustment of the stimulation impulse amplitude in relation to a determined capture threshold. This adjustment is obtained by a progressive reduction of the stimulation impulse amplitude level over several successive cardiac cycles, detection of the disappearance of the capture, and then reestablishment of the stimulation impulse amplitude at a level slightly greater than the threshold corresponding to the disappearance of capture. The disclosure of U.S. Pat. No. 5,411,533 is incorporated herein by reference.
As is generally understood by persons skilled in the art, "capture" is a cardiac event where there is a depolarization following and responsive to delivery of a stimulation impulse. The "capture threshold" is the minimal voltage level of the stimulation impulse that causes capture, namely the desired depolarization of the cardiac tissue at the stimulation site.